ijmb model questions vol1 2025 biology | Essay

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Question 1 View Details
The diagram shows a typical animal cell with its major organelles labelled.
Question Parts
(a)
Identify four organelles shown in the diagram and state the principal function of each.
(b)
Explain the pathway of protein synthesis from the DNA in the nucleus to the secretion of the protein outside the cell, using the organelles shown.
(c)
Based on the diagram, compare the relative size of mitochondria and ribosomes and discuss how their size relates to their function.
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Question 2 View Details
The diagram depicts the sequential stages of mitosis in a eukaryotic cell, with each stage clearly labelled.
Question Parts
(a)
List the four main stages of mitosis in the correct chronological order.
(b)
For each stage, describe the key cellular events that occur, referring to the structures shown in the diagram.
(c)
Explain how cytokinesis differs between animal and plant cells, using the diagram where appropriate.
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Question 3 View Details
The diagram shows a labelled model of a balanced daily diet plate according to the Nigerian dietary guidelines.
Question Parts
(a)
Identify the food groups represented by each coloured region of the plate and state the recommended proportion (percentage of the total plate) for each group.
(b)
Explain why inclusion of each food group is essential for human nutrition, citing at least one nutrient supplied by each group and its physiological role.
(c)
A 30‑year‑old male office worker consumes a diet that provides 2500 kcal per day. Using the recommended proportions from part (a), calculate the approximate energy (kcal) that should be obtained from each food group. Show your calculations.
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Question 4 View Details
The diagram shows the human respiratory system with the labelled components A–I. A – Nasal cavity B – Pharynx C – Larynx D – Trachea E – Primary bronchi F – Bronchioles G – Alveolar sac H – Pulmonary capillary network I – Diaphragm
Question Parts
(a)
Describe the complete pathway that air follows from the external environment to the site of gas exchange, naming each structure it passes through.
(b)
The partial pressure of oxygen in ambient air at sea level is 160 mmHg. Assuming water‑vapour pressure in the conducting airways is 47 mmHg and using the alveolar gas equation PAO₂ = FiO₂(PB – PH₂O) – (PaCO₂ / R) where FiO₂ = 0.21, PB = 760 mmHg, PaCO₂ = 40 mmHg and R = 0.8, calculate the alveolar oxygen partial pressure (PAO₂). Show all steps and state any assumptions made.
(c)
Using the diagram, explain how the structure of the alveolar wall promotes efficient gas exchange. Mention at least three distinct structural features.
(d)
A patient exhibits a ventilation‑perfusion (V/Q) mismatch in which 30 % of alveoli are perfused but not ventilated. Discuss the effect of this mismatch on arterial oxygen tension and propose one physiological compensation mechanism that the body may employ.
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Question 5 View Details
A researcher is studying the transport of glucose in the human small intestine after a meal rich in carbohydrates.
Question Parts
(a)
Explain the mechanism by which glucose is absorbed from the intestinal lumen into the enterocytes, including the role of sodium.
(b)
After absorption into enterocytes, describe the two main pathways by which glucose enters the bloodstream, indicating the transport proteins involved.
(c)
A patient has a genetic defect that reduces the activity of the Na⁺/K⁺‑ATPase in intestinal epithelial cells by 40 %. Predict qualitatively how this defect would affect the efficiency of glucose absorption and justify your answer.
(d)
Given that the normal rate of glucose absorption is 0.5 g per minute, estimate the new absorption rate in the patient described in (c) assuming the reduction in Na⁺/K⁺‑ATPase activity proportionally reduces the sodium gradient driving secondary active transport. Show your reasoning.
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Question 6 View Details
A laboratory investigation is carried out to compare the excretory efficiency of two freshwater fish species, Species X and Species Y, kept in identical aquaria.
Question Parts
(a)
Outline the main organs involved in nitrogenous waste excretion in freshwater fish and the form of nitrogenous waste they primarily eliminate.
(b)
The experiment measures the concentration of ammonia in the water after 24 h. Species X shows an increase from 0.02 mg L⁻¹ to 0.12 mg L⁻¹, while Species Y shows an increase from 0.02 mg L⁻¹ to 0.08 mg L⁻¹. Calculate the total amount of ammonia excreted by each species over the 24 h period, assuming each aquarium holds 100 L of water and the fish are the only source of ammonia.
(c)
Discuss two physiological or behavioural adaptations that could explain the observed difference in ammonia excretion between the two species.
(d)
If the water temperature is raised from 25 °C to 30 °C, explain how this change is likely to affect the rate of ammonia excretion in both species, citing the underlying biochemical principle.
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Question 7 View Details
A researcher is studying how the human body maintains internal stability when exposed to varying environmental conditions.
Question Parts
(a)
Define homeostasis and state the two principal types of feedback mechanisms that regulate it.
(b)
The subject is placed in a cold environment (5 °C) for 30 minutes. Explain the physiological responses that are activated to preserve core body temperature. In your answer identify the primary sensor, the integrating centre and the effectors, and describe both neural and hormonal components of the response.
(c)
During the same experiment the subject receives an intravenous infusion of 5 % dextrose, raising blood glucose by 2 mmol L⁻¹. Discuss how glucose homeostasis is restored, outlining the sequence of events, the role of insulin, and how negative feedback operates. Compare the time scales of the neural response described in part (b) with the hormonal response in this part.
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Question 8 View Details
A physiologist investigates the coordination of voluntary movement in a 20‑year‑old athlete during a complex jumping task.
Question Parts
(a)
Outline the neural pathway from the primary motor cortex to the skeletal muscles that execute the jump. In your answer describe the roles of upper motor neurons, lower motor neurons and the neuromuscular junction, and give the chronological sequence of events from cortical activation to muscle contraction.
(b)
After a 30‑minute high‑intensity sprint, the athlete’s jump height falls by about 15 %. Explain, using the concepts of motor‑unit recruitment, peripheral fatigue and proprioceptive feedback, why performance declines. Discuss how the central nervous system attempts to compensate for peripheral fatigue.
(c)
Design a practical experimental protocol to assess the contribution of the cerebellum to the coordination of the jumping task. Include (i) a method for transiently disrupting cerebellar function, (ii) the variables that would be measured, and (iii) the expected changes in performance if cerebellar coordination is impaired. Justify each step of your protocol.
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Question 9 View Details
A 22‑year‑old woman attends the reproductive health clinic complaining of irregular menstrual cycles for the past six months and difficulty conceiving. She reports cycles ranging from 35 to 55 days with occasional spotting. Her medical history is unremarkable.
Question Parts
(a)
Describe the normal hormonal events of the menstrual cycle, indicating clearly the phase in which ovulation occurs.
(b)
Explain how a disruption in the hypothalamic‑pituitary‑ovarian (HPO) axis could produce the menstrual pattern described, citing at least two possible endocrine disorders.
(c)
The couple is advised to undergo controlled ovarian hyperstimulation (COH) followed by in‑vitro fertilisation (IVF). (i) Outline the physiological basis for using gonadotropin‑releasing hormone (GnRH) agonists in COH. (ii) Discuss one major risk associated with this protocol.
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Question 10 View Details
A pedigree of a Nigerian family shows a rare autosomal recessive disorder caused by a mutation in the gene encoding enzyme X. The proband (individual V‑3) is affected, while both parents (IV‑2 and IV‑3) are phenotypically normal. No other affected individuals appear in earlier generations.
Question Parts
(a)
State the most probable genotype of the proband and of each parent, providing a brief justification based on the mode of inheritance shown in the pedigree.
(b)
If the proband marries an individual from the same population who is phenotypically normal, calculate the probability that their first child will be affected, assuming Hardy‑Weinberg equilibrium with a carrier frequency of 1/50 for this disorder.
(c)
The disease results from a point mutation that creates a premature stop codon in the coding region of enzyme X. Discuss two molecular mechanisms by which a cell can mitigate the deleterious effect of such nonsense mutations.
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